PHYKPL encodes 5-phosphohydroxy-L-lysine phospho-lyase, a mitochondrial enzyme that catalyzes the pyridoxal phosphate-dependent breakdown of 5-phosphohydroxy-L-lysine into ammonia, inorganic phosphate, and 2-aminoadipate semialdehyde. This enzyme functions as a key component in the catabolism of hydroxylysine residues derived from collagen degradation, connecting extracellular matrix turnover to lysine catabolism and energy metabolism. Despite being classified in the aminotransferase III family, PHYKPL functions as an ammoniophospholyase rather than a transaminase. Loss-of-function mutations cause phosphohydroxylysinuria, a benign metabolic condition characterized by elevated urinary 5-phosphohydroxylysine without apparent clinical symptoms.
Definition: Catalysis of the reaction (5R)-5-phosphooxy-L-lysine + H2O = (S)-2-amino-6-oxohexanoate + NH4+ + phosphate
Justification: Specific molecular function term needed for PHYKPL enzymatic activity (EC 4.2.3.134), currently only general lyase term available
Definition: The chemical reactions and pathways resulting in the breakdown of 5-phosphohydroxy-L-lysine, a phosphorylated derivative of hydroxylysine
Justification: Specific metabolic process for this branch of lysine catabolism involving collagen-derived hydroxylysine
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: Annotated as mitochondrial based on UniProt subcellular location (ECO:0000305 curator inference). NOTE: PMID:22241472 (Veiga-da-Cunha 2012) did NOT experimentally confirm mitochondrial localization β it reported a TargetP/PSORT II *prediction* of cytosolic localization and noted the contradiction with the curated mitochondrial assignment. Per PR #749 review feedback, the earlier summary's claim of "experimental confirmation" of mitochondrial localization was incorrect. The ACCEPT action remains defensible because the protein handles a metabolite (5-phosphohydroxy-L-lysine) catabolized via pathways with mitochondrial counterparts and UniProt's curator inference is reasonable, but the annotation is currently supported by prediction/curator inference rather than direct microscopy or proteomics evidence. Supporting Evidence: file:human/PHYKPL/PHYKPL-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000305|PubMed:22241472} file:human/PHYKPL/PHYKPL-deep-research-lite.md See deep research file for comprehensive analysis |
| GO:0005759 mitochondrial matrix | IEA GO_REF:0000117 | ACCEPT | Summary: Correctly annotated. The mitochondrial matrix localization is appropriate for this enzyme that participates in amino acid catabolism, and is consistent with the experimental characterization in PMID:22241472. |
| GO:0008483 transaminase activity | IEA GO_REF:0000002 | REMOVE | Summary: Incorrect annotation. PMID:22241472 explicitly states: "Unlike AGXT2, AGXT2L1 and AGXT2L2 did not act as transaminases." Despite belonging to the aminotransferase III family, PHYKPL functions as an ammoniophospholyase, not a transaminase. The UniProt entry also cautions: "Does not seem to possess aminotransferase activity." Supporting Evidence: PMID:22241472 Unlike AGXT2, AGXT2L1 and AGXT2L2 did not act as transaminases |
| GO:0016829 lyase activity | IEA GO_REF:0000043 | MODIFY | Summary: Too general. The enzyme is indeed a lyase (EC 4.2.3.134), but more specifically a carbon-oxygen lyase acting on phosphates. PMID:22241472: "The phosphorylation product made by this enzyme was metabolized by AGXT2L2, which converted it to ammonia, inorganic phosphate, and 2-aminoadipate semialdehyde." Proposed replacements: carbon-oxygen lyase activity, acting on phosphates |
| GO:0030170 pyridoxal phosphate binding | IEA GO_REF:0000002 | ACCEPT | Summary: Correctly annotated. PMID:22241472: "AGXT2L1 and AGXT2L2 catalyzed the pyridoxal-phosphate-dependent breakdown of phosphoethanolamine and 5-phosphohydroxy-L-lysine." The enzyme requires PLP as an essential cofactor. Supporting Evidence: PMID:22241472 putative pyridoxal-phosphate-dependent enzymes encoded by vertebrate genomes file:human/PHYKPL/PHYKPL-deep-research-falcon.md AGXT2L2 was purified as a **yellow PLP-binding protein**, consistent with PLP cofactor association |
| GO:0005515 protein binding | IPI PMID:21044950 Genome-wide YFP fluorescence complementation screen identifi... | REMOVE | Summary: Generic protein binding annotation from a high-throughput screen (YFP complementation for telomere signaling regulators). The interaction partner is POT1 (telomere protein), which seems biologically unlikely given PHYKPL's mitochondrial localization and metabolic function. This is likely a false positive or artifact. The generic "protein binding" term provides no functional insight. Supporting Evidence: PMID:21044950 Epub 2010 Nov 2. Genome-wide YFP fluorescence complementation screen identifies new regulators for telomere signaling in human cells. |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | REMOVE | Summary: Generic protein binding from proteome-scale interactome mapping. Shows interactions with USO1 (vesicle transport) and VAC14 (PI signaling), which are not obviously related to PHYKPL's metabolic function. These high-throughput interactions lack validation and the generic term provides no functional insight. Supporting Evidence: PMID:25416956 A proteome-scale map of the human interactome network. |
| GO:0005515 protein binding | IPI PMID:29892012 An interactome perturbation framework prioritizes damaging m... | REMOVE | Summary: Generic protein binding from an interactome perturbation study. Shows interactions with VAC14 and LNX2, neither obviously related to lysine catabolism. High-throughput data without validation, and the generic term adds no functional information. Supporting Evidence: PMID:29892012 Jun 11. An interactome perturbation framework prioritizes damaging missense mutations for developmental disorders. |
| GO:0005515 protein binding | IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari... | REMOVE | Summary: Generic protein binding from a study on genetic variants disrupting protein interactions. Shows interaction with LNX2, not obviously related to PHYKPL function. Generic term provides no functional insight. Supporting Evidence: PMID:31515488 Extensive disruption of protein interactions by genetic variants across the allele frequency spectrum in human populations. |
| GO:0042802 identical protein binding | IPI PMID:16189514 Towards a proteome-scale map of the human protein-protein in... | ACCEPT | Summary: Self-interaction detected in high-throughput screen. This is biologically plausible as UniProt states: "Homotetramer" based on similarity to related enzymes. The tetramerization is likely functionally relevant for enzymatic activity, as is common for PLP-dependent enzymes. Supporting Evidence: file:human/PHYKPL/PHYKPL-uniprot.txt Subunit: Homotetramer. {ECO:0000250|UniProtKB:P22256} PMID:16189514 Towards a proteome-scale map of the human protein-protein interaction network. |
| GO:0042802 identical protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | ACCEPT | Summary: Self-interaction confirmed in proteome-scale interactome map. Consistent with the known homotetramer structure of PHYKPL, supporting the functional oligomerization. Supporting Evidence: PMID:25416956 A proteome-scale map of the human interactome network. |
| GO:0042802 identical protein binding | IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari... | ACCEPT | Summary: Self-interaction detected in genetic variant study. Consistent with homotetramer formation required for enzymatic function. Supporting Evidence: PMID:31515488 Extensive disruption of protein interactions by genetic variants across the allele frequency spectrum in human populations. |
| GO:0042802 identical protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | ACCEPT | Summary: Self-interaction confirmed in reference human binary interactome map. Further supports the homotetramer structure necessary for enzymatic function. Supporting Evidence: PMID:32296183 Apr 8. A reference map of the human binary protein interactome. |
| GO:0005759 mitochondrial matrix | TAS Reactome:R-HSA-5696408 | ACCEPT | Summary: Original Reactome pathway reference cannot be validated due to missing cached file. However, mitochondrial matrix localization is correct based on other evidence. |
| GO:0042219 modified amino acid catabolic process | IDA PMID:22241472 Molecular identification of hydroxylysine kinase and of ammo... | NEW | Summary: PMID:22241472 demonstrates that PHYKPL catalyzes the breakdown of 5-phosphohydroxylysine, a phosphorylated derivative of hydroxylysine from collagen. Term updated from obsolete GO:0046948 (hydroxylysine catabolic process) to GO:0042219 (modified amino acid catabolic process) since the original term was obsoleted due to no evidence of the process existing. Supporting Evidence: PMID:22241472 The phosphorylation product made by this enzyme was metabolized by AGXT2L2, which converted it to ammonia, inorganic phosphate, and 2-aminoadipate semialdehyde file:human/PHYKPL/PHYKPL-deep-research-falcon.md This reaction places PHYKPL in a defined pathway for **hydroxylysine catabolism** downstream of a 5-hydroxylysine kinase (AGPHD1/HYKK). |
| GO:0016838 carbon-oxygen lyase activity, acting on phosphates | IDA PMID:22241472 Molecular identification of hydroxylysine kinase and of ammo... | NEW | Summary: NEW ANNOTATION: More specific than general "lyase activity". PHYKPL is a phospho-lyase that cleaves carbon-oxygen bonds by eliminating phosphate, as demonstrated in PMID:22241472. Supporting Evidence: PMID:22241472 AGXT2L2, which converted it to ammonia, inorganic phosphate, and 2-aminoadipate semialdehyde file:human/PHYKPL/PHYKPL-deep-research-falcon.md Kinetic parameters reported for recombinant human AGXT2L2 acting on 5PHyl include: - **Km(5PHyl) = 16.9 Β± 4.5 ΞΌM** - **Vmax = 256 Β± 15 nmolΒ·minβ»ΒΉΒ·mgβ»ΒΉ protein** |
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Download this section (compressed HTML)Q: What regulates PHYKPL expression under different metabolic conditions or during collagen remodeling?
Suggested experts: Metabolic biochemists, ECM biologists
Q: Are there tissue-specific differences in PHYKPL expression or activity that correlate with collagen turnover rates?
Suggested experts: Tissue metabolism specialists
Q: Why does phosphohydroxylysinuria have no apparent clinical phenotype despite metabolite accumulation?
Suggested experts: Clinical geneticists, Metabolic disease specialists
Q: Does PHYKPL interact with other enzymes in the lysine catabolic pathway to form metabolic complexes?
Suggested experts: Mitochondrial biochemists
Q: What is the structural basis for the enzyme's substrate specificity and PLP-dependent mechanism?
Suggested experts: Structural biologists, Enzymologists
Experiment: Crystallize human PHYKPL with substrate analogs and PLP to determine 3D structure
Hypothesis: Structure will reveal unique active site features explaining substrate specificity for phosphohydroxylysine
Type: Structural biology
Experiment: Compare metabolite profiles in PHYKPL knockout vs wild-type cells under high collagen turnover conditions
Hypothesis: Loss of PHYKPL will lead to accumulation of 5-phosphohydroxylysine and reveal alternative catabolic routes
Type: Metabolomics
Experiment: Identify PHYKPL protein interaction partners in mitochondrial matrix using proximity labeling (BioID)
Hypothesis: PHYKPL forms complexes with other lysine catabolic enzymes for efficient substrate channeling
Type: Proteomics
Experiment: Analyze PHYKPL expression across tissues and developmental stages using single-cell RNA-seq
Hypothesis: PHYKPL expression correlates with tissue collagen content and turnover rates
Type: Expression profiling
Experiment: Use 13C-labeled hydroxylysine to trace flux through PHYKPL pathway in various cell types
Hypothesis: Flux through PHYKPL varies with cell type and metabolic state
Type: Metabolic flux analysis
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